“Chemical Reactions and Equations: Exam Practice Pack” is available to Standard subscribers.
In an exam, chemical equations are worth easy marks, if you are quick and you check your work. This pack gives you two exam skills, six problems, a Python checker for your balancing, and timed papers. One paper is in the Standard pack, and a longer one with worked solutions is for Premium.
Exam skill: balance fast and check by counting: Balance with a table of atoms. List each atom and make the sides equal one atom at a time. Start with the atom in the fewest formulas, leave hydrogen and oxygen for last, and always count again.
Exam skill: name the type, the products and the energy: A reaction is named by what happens to its substances. Two or more join (combination), or one splits (decomposition). An element takes the place of another (displacement), or two compounds swap partners (double displacement). Look for heat, light, a gas or a precipitate to confirm.
Exam skill: reacting masses and the limiting reactant: Mass questions carry many marks. Go from grams to moles, use the ratio of the coefficients, then go back to grams. When two masses are given, find which reactant runs out first: it decides the product. Heat questions use Q = m c ΔT.